1. Field of the Invention
This invention relates to storage-stable porphin compositions, with particular preference to hematoporphyrin-based compositions, their manufacture and their use as photoimaging agents and in photodynamic therapy.
2. Background Materials
Porphins are nitrogen-containing polyheterocyclic compounds which include porphyrins and chlorins. It has been recognized that some porphyrins and chlorins have a natural tendency to preferentially accumulate in neoplastic tissues relative to normal tissue. It has also been recognized that the porphins so accumulated, being colored and/or fluorescent, can serve as imaging agents for detecting the neoplastic masses. The porphin materials themselves often are relatively harmless and nontoxic but when exposed to light in some cases can become very toxic to surrounding tissues. Thus, the accumulated porphins can be preferentially phototoxic to the tumors in which they accumulate. The general technique has come to be known as photodynamic therapy or "PDT". Lasers are the preferred sources of the 630 nm light which is generally employed.
Hematoporphyrin and materials derived from hematoporphyrin have been identified as advantageous materials in this diagnosis technique and therapy. In the 1960's, Lipson and coworkers developed a material known as "hematoporphyrin derivative" ("HPD") having enhanced localization properties. (See, for example, J. NATL. CANCER INST. 26, (1961) 1) Thereafter, Dougherty and coworkers and others applied HPD in combination with light for selective tumor destruction. (See, for example, J. NATL. CANCER INST., 52 (1974) 1333)
A recent article by Hubert van den Bergh appearing at page 430 of the May, 1986 issue of CHEMISTRY IN BRITAIN provides a concise review of the history of this technology. It and the references it reviews describe the early work of Policard (C.R. SOC. BIOL. PARIS, 91, (1924) 1423), Auler and Banzer (ABH. KREBSFORSCH., 53, (1942) 65) and Figge (UNIV. MED. BULL., 26, (1942) 165), which noted that porphins were phototoxic and that this type of compound preferentially accumulated in neoplastic tissues, as well as more recent studies with porphins and in particular HPD as clinically effective anti-tumor agents. A conference entitled "Porphyrin Photosensitization Workshop" held on June 26 and 27, 1986 at the Sheraton Universal City Hotel (hereinafter the "PPW") and the posters there presented also provide a recent overview of the present state of this therapy.
HPD is produced from hematoporphyrin by the process of treating hematoporphyrin with acetic acid and sulfuric acid and thereafter dissolving the acetylated product (referred to as HPA) in alkali to yield HPD. HPD is also referred to in the field by the tradename "Photofrin I" associated with a widely distributed HPD preparation. Workers have made efforts to upgrade the performance of acid-formed conventional HPD by gel filtration purification to give a purified HPD product referred to as "Photofrin II" (see, Dougherty, et al in PORPHYRINS IN TUMOR THERAPY (Andreoni, et al, eds), pp 23-35, Plenum Press, New York and London). Another approach to modifying HPD has involved drying the HPD and then heat-treating the solid at 160.degree. C. for two hours (see Moan, et al PHOTOCHEMISTRY AND PHOTOBIOPHYSICS 9, (1985) 253-261).
HPD is a complex mixture of materials. (See, for example, van den Bergh, CHEMISTRY IN BRITAIN, noted above and G. Bottiroli, Poster "Influence of Interactions with Cellular Structures on HPD Aggregation State" at "PPW") The Photofrin II material is a mixture as well. (See, M.W. Berns, et al, Poster Cellular and Spectroscopic Studies on HPD and Its Components, at PPW) HPD contains at least 15 components (van den Bergh, CHEMISTRY IN BRITAIN, noted above) including hematoporphyrin itself (HP, structure 1, below), protoporphyrin (PP, structure 1, below), dihematoporphyrin ether (structure 2, below) or dihematoporphyrin ester (structure 3, below), and hydroxyethylvinyldeuteroporphyrin (HVD, structure 1, below). ##STR1##
HPD and the Photofrin II material have been the subjects of numerous studies to attempt to unambiguously identify their active components. These studies have been rendered particularly difficult by the facts that (1) porphin type compounds give very indistinct infrared spectra, (2) porphin type compounds tend to aggregate into a variety of forms and conformations, and (3) the porphins of most interest often contain a plurality of each of several functional groups some of which can be in one form or state of combination and some in another.
Various workers in the field have suggested that either or both of the ether of structure 2 or the ester of structure 3 is the primary contributor to HPD activity. (See, for example, European Patent Application 84/1382 and J. Dougherty, et al, "The Structure of the Active Component of Hematoporphyrin Derivative", appearing at PROG. CLIN. BIOL. RES., 1984, 170, 301-314 --which propose Bis-1-[8-(1-hydroxyethyl)-deuteroporphyrin-3-yl] ethyl ether, stucture 2, above; and D. Kessel "Proposed Structure of the Tumor-Localizing Component of Hematoporphyrin Derivative" appearing at PHOTODYNAMIC THERAPY OF TUMORS AND OTHER DISEASES (G. Jori and C. Perria, eds) pp. 1-7, 1985--which proposes the ester of structure 3, above, and B.D. Musselman, et al, Poster, "Ethers and Esters Linked Dimers of Hematoporphyrin in Hematoporphyrin Derivative" at PPW--which proposes a mixture or ether and ester dimers.
Other studies have suggested that the active species in HPD could be an aggregate of porphyrins, such as an aggregate of DHE units or the like. (See, for example, A. D. Ward, Poster, "The Structure, Conformational Changes, and Mechanism of action of Photofrin II, at PPW; G. Bottiroli, et al, Poster, noted above; P. A. Scourides, et al, Poster, "The Nature of Hematoporphyrin Derivative (HPD) Aggregates" at PPW. But, as already noted, difficulties inherent in the porphin materials have rendered illusive a definite answer.
A fourth characteristic of the porphin compounds has also interfered with clear understanding of their exact structure and, more importantly, has interfered with their use as neoplastic tissue imaging and photodynamic therapy agents. This characteristic is that the known preparations are unstable. They vary in composition from preparation to preparation and have been observed to degrade with time to inactive side products. For example, the Photofrin II material when newly prepared contains about 75% of its active species. At room temperature, this material decreases to 50-55% of the total within a few hours. In our hands, HPD or Photofrin II can be purified via membrane filtration techniques to a purity of about 90% active material. Again, this material is seen to degrade to 50-55% active material in less than 24 hours at room temperature. In response to this problem, the Photofrin materials and like porphin-based photoimaging and PDT agents are commonly shipped at dry ice temperature and stored as frozen solids and only warmed to room temperature immediately prior to use.
It is an object of this invention to provide porphin-based (and especially hematoporphyrin-based) preparations which are relatively more thermally and temporally stable than preparations shown in the art and which maintain high levels of active tumor imaging and photodynamic therapy agents. It is a further object of this invention to provide processes for producing such materials and methods of diagnosis and therapy employing such materials.